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If you’ve worked with acrylic or certain other plastics before, you might be aware that they bond best with solvent-based adhesives. Solvent-based cements provide the least mess and cleanest bonds if applied with care, helping your projects and enclosures look even better.

Solvent cements are best applied via a capillary action, where you assemble the to-be-bonded plastic pieces and let small amounts of the liquid flow into the joint. There are two main types of applicators you can use – squeeze-bottles and syringes.

Going back more than a decade, I used to purchase my plastic materials and supplies over at Canal Street, in NYC. There were specialty plastics shops that had everything I needed, and Pearl Paint carried a few plastic-working tools and accessories as well. But a couple of years ago when I went back, I found higher prices and almost no selection.

Looking online, almost all online plastics suppliers do carry several sizes of syringes and applicator bottles, but their prices seem a bit steep, even with quantity discounts. Because of this I started ordering my applicator syringes from industrial suppliers. Syringes are quite easy to find, but blunted applicator needles can be a little harder to come by.

Unless you already have a preference, I would recommend 10cc syringes. This size is easy to find, and reasonably economical. Plus this is a handy size for other uses, such as topping-off small water-cooling reservoirs. Packs of 10 are available via McMaster Carr (7510A653) and other suppliers, and make sure to get the kind with Luer Lock tips. You’ll usually save a few bucks if you don’t need graduated barrels.

There are many options for blunted dispensing needles, allowing you to choose from different materials, diameters, and lengths to suit your needs. Stainless steel needles, even of the disposable type, are quite durable and should last some time if you make sure to flush them after each use.

For my own projects, I have two reusable Luer Lock needles, 24 gauge x 1/4-inch long and 22 gauge x 2-inches long, and a pack of 26 gauge x 1-1/2-inch long. McMaster part numbers are 6710A29, 6710A74, and 75165A762 respectively. Thinner needles are more fragile, which is why I opted for disposable ones rather than the reusable kind. Plus, I am far less hesitant to bend them to improve access to hard-to-reach joints or repairs.

Whatever you do, avoid using pointed hypodermic needles. Safety hazards aside, they are messy and imprecise to use for dispensing solvent cement and other liquids.

Stuart Deutsch is a tool enthusiast, critic, and collector, and writes his passion at ToolGuyd.

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Why are the pointed hypodermic ones any worse than the blunted ones? I have never experienced any issue with them. And if you are worried about the pokey bits poking, just sand it down.

http://toolguyd.com Stuart Deutsch

Not all pointed needles will be bad, but many such tip profiles dispense fluids with less control and precision. Instead of solvent flowing forward towards the joint, some droplets may spill out horizontally. And since solvent cements can mar plastic finishes, this should be minimized.

Have you ever tried sanding a hypodermic needle to blunt it? Grinding probably wouldn’t be any easier.

Although it’s not a great practice, syringes with hypodermic needles will still get the job done in a pinch.

David s

What about welding pla or abs?

http://toolguyd.com Stuart Deutsch

Different plastics generally require different solvent cements. I’m not sure about PLA, but offhand I know there are formulas for acrylic, polycarbonate, ABS, and styrene. Some cements are more viscous and should be used with thicker gauge dispensing needles. Plastic welding cement manufacturers will generally provide usage recommendations.

Matt Richardson

Thanks for this great advice about syringes! I’ve recently started using solvents to bond acrylic and have been using a squeeze bottle with needle on the end, which has been tough to control. I’ll definitely put in an order for these syringes. Thanks again!

http://toolguyd.com Stuart Deutsch

You’re very welcome, and I’m glad to have helped!

Don’t throw the squeeze bottle away, you never know if/when it might come in handy. And if the squeeze bottle came with a Luer-Lock needle, you might be able to use it with a new syringe.

http://www.superpants.net Superpants

I have found in the UK that first aid suppliers such as SP supplies are much cheaper for syringes than the hobby or industrial suppliers

http://tastymonkeybrains.blogspot.com/ MonkeyBrains

Neat idea! What do you use to flush the acrylic cement?

http://toolguyd.com Stuart Deutsch

There are a couple of ways this can be done. One way is to keep a dedicated flushing syringe filled with water (distilled will work best), and use it to push clean water through applicator tips or needles. A couple of CCs usually does the trick. This can be followed by passing air through the needles with another dedicated syringe to help dry them out.

Mike Jusko

If you want to remove the point from the standard luer-lock type syringe try this. Find a section of bare wire that just fills the bore of the needle you want to blunt. Thread the wire in (I pull out the plunger and use the syringe barrel for a grip). The wire should protrude slightly. Bend the wire at the tip, then using a very fine diamond whetstone, grind off the whole thing down, a millimeter or so. The wire will keep you from developing an inside burr which breaks up flow. then you can clean up the outsideby rolling the barrel over the whetstone backwards, it works best with water as a lube. I can do several this way every minute or so.

Also if you have any nursing friends: there is a relativly new product in the health-care area. It is a safety IV luer lock plastic infusion needle. It is made of a hard slick plastic like delrin or PEEK that is translucent and somewhat blunted. Most adhesives don’t stick and it cleans up a lot easier than stainless.

I have been trying to create a bubble free join in small pieces of face to face acrylic, with little success. A few things I have already found have helped, is there anything else?
Never solvent weld under 65 F!
Use a very fine spacer (needle) to create a small gap to aid capillary action and wait 20 seconds before removing!
I have seen a video using a chemical to aid capillary action and reduce bubbles – does anyone know what this may be? http://www.youtube.com/watch?v=XFpMeBQEmrI
– I was thinking it may be an alcohol, meths maybe, starting the solvent off?
Also, I am using a dichloromethane solvent and the health and safety problems are off the charts; even in a well ventilated area will a mask protect from the fumes (carbon monoxide)?
Many Thanks